1. Field of the Invention
This invention relates to a semiconductor device having a semiconductor chip mounted on a circuit board by flip chip bonding and, more particularly, to a multi-device having a plurality of semiconductor chips mounted and a method of manufacturing the same.
2. Description of the Related Art
A semiconductor device shown in, for example, FIGS. 5 and 6 is known as this kind of semiconductor device.
FIG. 5 is a plan view showing the semiconductor device and FIG. 6 is a cross-sectional view of the semiconductor device as seen along a line C-C′ of FIG. 5.
The semiconductor device comprises a wiring board 16. First to fourth semiconductor chips 17, 18, 19 and 20 are arranged on the wiring board 16. One-end portions of heat radiating members (hereinafter called metal plates) 21, 22, 23 and 24 are bonded to top surface portions of the first to fourth semiconductor chips 17 to 20, respectively, and the other-end portions thereof are bonded to the wiring board 16. The semiconductor chips 17 to 20 and the heat radiating members 21 to 24 are sealed by thermosetting resin 25.
The first and second semiconductor chips 17 and 18 are control ICs. The third and fourth semiconductor chips 19 and 20 are MOSFETs. Each of the third and fourth semiconductor chips (MOSFETs) 19 and 20 comprises a gate electrode and a source electrode on a top surface and a drain electrode on a back surface. The metal plates 23 and 24 connected to the third and fourth semiconductor chips (MOSFETs) 19 and 20 serve as passages through which heat generated by the semiconductor chips 19 and 20 are radiated to outside and play a role of electrically connecting the back surfaces of the semiconductor chips 19 and 20 to the wiring board 16.
The semiconductor chips 17 to 20 are connected to the wiring board 16 by flip chip bonding using high-melting-point solder 26. The metal plates 21 to 24 are bent in a shape of gull wing and connected to the back surfaces of the semiconductor chips 17 to 20, respectively, by low-melting-point solder 27 and to the wiring board 16 by the low-melting-point solder 27.
Use of the solders 26 and 27 having different melting points prevents the flip chip bonding portions of the semiconductor chips 17 to 20 from melting during the soldering of the metal plates 21 to 24.
The metal plates 21 to 24 may be bonded to the back surfaces of the semiconductor chips 17 to 20 and the wiring board 16 with conductive paste containing thermosetting resin. In this case, however, the heat radiation efficiency of the semiconductor chips 17 to 20 is lowered.
Moreover, to radiate heat of the semiconductor chips, radiation covers are provided on the flip chip semiconductor chips. In this example, each of metallic radiation covers is attached onto the semiconductor chip and comprises four feet.
As the assembling method, the semiconductor chips are first mounted on the wiring board by the flip chip bonding and then the radiation covers are provided on the semiconductor chips.
Materials having preferable thermal conductivity such as copper/molybdenum, copper/tungsten or the like are used for the radiation covers. The semiconductor chips and the radiation covers are bonded with a heat-conducting adhesive or solder. The feet of the radiation covers are bonded to the wiring board with an adhesive or solder.
If a large current flows to the semiconductor device having such a structure, a large quantity of heat is generated from the semiconductor chips. If the semiconductor device is applied to a power MOSFET having electrodes on the back surfaces of the semiconductor chips, solder needs to be employed for bonding of each of semiconductor chips as disclosed in the prior art. The semiconductor device is sealed with resin after the semiconductor chips and the radiation covers are mounted on the wiring board (see, for example, Jpn. Pat. Appln. KOKOKU Publication No. 5-73066).
In general, the semiconductor device is sealed with a kind of resin. A thermosetting epoxy resin is often used as this resin in view of manufacturing costs and the resistance to heat. The resin is supplied to the semiconductor device by transfer mold or printing (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2001-177010).
In the other structure of the semiconductor device, a flat plate is connected to the back surface of the device to radiate heat. A heat radiating portion can be secured but this structure cannot be applied to a MOSFET allowing electrodes to be taken from the back surface (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 8-250652).
In the prior art, however, since the semiconductor chips and the metal plates are sealed with resin and then the resin on the metal plates is removed to expose the metal plates, load may be applied to the flip chip bonding portions of the semiconductor chips located under the metal plates and the flip chip bonding portions may be thereby damaged.
In addition, since a plurality of metal plates are attached separately to the wiring board, the angle of attachment of the metal plates becomes irregular and the degree of parallel becomes lower. Therefore, the resin can hardly be removed from the metal plates.